This season I noticed a vibration at idle when in neutral. I was concerned that it was the gimbal bearing or a U joint. I just pulled the drive and everything looks fine . I checked the engine alignment and I can spin the alignment tool with two fingers. If I grease the alignment tool and insert it and look at the pattern that the splines of the engine coupler left on it, I would say it is maybe a millimeter off. Its almost even all around but it dose favor one side. Its that close that I don't want to mess with it.

Also I did a lot of work to the boat . It is very solid and I have solid motor mounts. maybe it is just normal and I am just noticing it now that everything on the boat is tight.

Any thoughts

Make sure you recheck the alignment after turning the engine 180 degrees. I actually do mine in 4 places, every 90 degrees. Ive seen couplers out as much as .025.

if the coupler is out what dose that mean ????

I know what you are saying but is this a consern that requires a replacment of the coupler.

Well, the bad news is it requires removal of the engine. The coupler bolt holes can be drilled oversize and the coupler moved until its centered and then pined in place. I use a zero tolerence shaft that fits the primary bore of the coupler spline and a dial indicator to make sure its close before I put the flywheel housing on. They are usually pretty close but not always. I dont think they move any with time or wear, just made that way. Typical production parts. A different one might be right on.

Now I'm wondering if I really screwed up?? I recently put new engines(502/bravo's) in my boat. The couplers and flywhells were in good shape so I reused them. The bolts that secure the couplers to the flywheels seemed like a snug fit so I didn't worry too much about the coupler not being aligned right....and I'm not sure that I got the port/starboard back on the respective flywheels.
Now the engines run great but I have a severe knocking from the port engine from the transom area. I was thinking it was just a ujoint going bad but now I'm wondering if my couplers might be slightly off center and causing the noise.
A lot harder to realign the coupler than replace a bad u joint.
How important is it to check the runout on the couplers? or do the stock bolts usually get you close enough??